Cellular communication system and method for broadcast communication

ABSTRACT

A cellular communication system ( 100 ) is arranged to support a single cell identifier reuse pattern using a first communication. Management logic ( 146 ) comprises broadcast mode logic ( 150 ) arranged to support a common cell identifier reuse pattern for broadcast transmissions amongst a cluster of communication cells using a second communication. A plurality of wireless serving communication units are operably coupled to the management logic. At least one wireless communication unit comprises logic arranged to support a unicast communication using a first communication cell identifier and logic arranged to support broadcast communication using a common cell identifier ( 215 ) to be used by the wireless communication unit in receiving broadcast communication across the cluster of communication cells.

RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.11/602,729, filed Nov. 20, 2006, which is incorporated by reference inits entirety herein.

This application is related to co-pending and co-owned U.S. patentapplication Ser. No. 13/159,622, entitled Cellular Communication SystemAnd Method For Broadcast Communication and filed on even date herewith,which is incorporated by reference in its entirety herein.

This application is related to co-pending and co-owned U.S. patentapplication Ser. No. 13/159,747, entitled Cellular Communication SystemAnd Method For Broadcast Communication and filed on even date herewith,which is incorporated by reference in its entirety herein.

This application is related to co-pending and co-owned U.S. patentapplication Ser. No. 13/159,832, entitled Cellular Communication SystemAnd Method For Broadcast Communication and filed on even date herewith,which is incorporated by reference in its entirety herein.

FIELD OF THE INVENTION

The invention relates to utilisation of communication resources incellular communication systems and in particular, but not exclusively,to supporting broadcast communication in a time-division duplex 3^(rd)Generation Partnership Project (3GPP) cellular communication system.

BACKGROUND OF THE INVENTION

Currently, 3rd generation cellular communication systems are beingrolled out to further enhance the communication services provided tomobile phone users. The most widely adopted 3rd generation communicationsystems are based on Code Division Multiple Access (CDMA) and FrequencyDivision Duplex (FDD) or Time Division Duplex (TDD) technology. In CDMAsystems, user separation is obtained by allocating different spreadingand/or scrambling codes to different users on the same carrier frequencyand in the same time intervals. This is in contrast to time divisionmultiple access (TDMA) systems, where user separation is achieved byassigning different time slots to different users.

In addition, TDD provides for the same carrier frequency to be used forboth uplink transmissions, i.e. transmissions from the mobile wirelesscommunication unit (often referred to as wireless subscribercommunication unit) to the communication infrastructure via a wirelessserving base station and downlink transmissions, i.e. transmissions fromthe communication infrastructure to the mobile wireless communicationunit via a serving base station. In TDD, the carrier frequency issubdivided in the time domain into a series of timeslots. The singlecarrier frequency is assigned to uplink transmissions during sometimeslots and to downlink transmissions during other timeslots. Anexample of a communication system using this principle is the UniversalMobile Telecommunication System (UMTS). Further description of CDMA, andspecifically of the Wideband CDMA (WCDMA) mode of UMTS, can be found in‘WCDMA for UMTS’, Harri Holma (editor), Antti Toskala (Editor), Wiley &Sons, 2001, ISBN 0471486876.

In a conventional cellular system, cells in close proximity to eachother are allocated non-overlapping transmission resources. For example,in a CDMA network, cells within close proximity to each other areallocated distinct spreading codes (to be used in both the uplinkdirection and the downlink direction). This may be achieved by, forexample, employing the same spreading codes at each cell, but adifferent cell specific scrambling code. The combination of these leadsto effectively distinct spreading codes at each cell.

In order to provide enhanced communication services, the 3rd generationcellular communication systems are designed to support a variety ofdifferent and enhanced services. One such enhanced service is multimediaservices. The demand for multimedia services that can be received viamobile phones and other handheld devices is set to grow rapidly over thenext few years. Multimedia services, due to the nature of the datacontent that is to be communicated, require a high bandwidth.

Typically, in such cellular systems that employ a single carrierfrequency, a wireless subscriber unit is ‘connected’ to one wirelessserving communication unit, i.e. one cell. Other cells in the networktypically generate interfering signals to the wireless subscriber unitof interest. Due to the presence of these interfering signals adegradation of the maximum achievable data rate, which can be maintainedto the wireless subscriber unit, is typical.

The typical and most cost-effective approach in the provision ofmultimedia services is to ‘broadcast’ the multimedia signals, as opposedto send the multimedia signals in an uni-cast (i.e. point-to-point)manner. Typically, tens of channels carrying say, news, movies, sports,etc. may be broadcast simultaneously over a communication network.

As radio spectrum is at a premium, spectrally efficient transmissiontechniques are required in order to provide users with as many broadcastservices as possible, thereby providing mobile phone users (subscribers)with the widest choice of services. It is known that broadcast servicesmay be carried over cellular networks, in a similar manner toconventional terrestrial Television/Radio transmissions.

Technologies for delivering multimedia broadcast services over cellularsystems, such as the Mobile Broadcast and Multicast Service (MBMS) forUMTS, have been developed over the past few years. In these broadcastcellular systems, the same broadcast signal is transmitted overnon-overlapping physical resources on adjacent cells within aconventional cellular system. Consequently, at the wireless subscriberunit, the receiver must be able to detect the broadcast signal from thecell it is connected to. Notably, this detection needs to be made in thepresence of additional, potentially interfering broadcast signals,transmitted on the non-overlapping physical resources of adjacent cells.

In addition, digital video broadcasting (DVB) technologies have recentlyevolved and are targeted at delivering broadcast video to mobilehandheld (DVB-H) terminals. Typically, all wireless infrastructuretransmitters in such networks operate as wireless ‘repeaters’. Hence, aseparate and distinct technology, usually a cellular phone technology,is used to provide uplink and downlink uni-cast signals (which arerequired to carry control signalling and uplink user traffic) tofacilitate broadcast communications to the DVB-H terminal using DVB.Although it is possible to integrate DVB-H receivers for such broadcastsystems into a mobile phone, the cost of such ‘dual-mode’ devices willbe significant.

Thus, all known techniques proposed or implemented for broadcastwireless transmissions require either separate spectrum dedicated forbroadcast purposes inefficiently. Alternatively, the known techniquespropose or implement duplicate circuitry in the mobile receiver toreceive distinct broadcast and uni-cast transmissions at respectivefrequencies, again somewhat inefficiently with respect to broadcasttransmissions.

Thus, typically in a cellular network, in order to achieve the highbandwidths envisaged for broadcast transmissions, there is a requirementto mitigate interference from neighbouring cells in order to achieve thehigh throughput rates required for a broadcast transmission.

EP-A-1361770 discloses a broadcast wireless communication system.

Consequently, current techniques are suboptimal. Hence, an improvedmechanism to address the problem of supporting broadcast transmissionsover a cellular network would be advantageous. In particular, a systemallowing for the provision of broadcast transmissions in an UTRA TDDsystem to co-exist with the existing UTRA-TDD system would beadvantageous.

SUMMARY OF THE INVENTION

Accordingly, the invention seeks to mitigate, alleviate or eliminate oneor more of the abovementioned disadvantages singly or in anycombination.

According to a first aspect of the invention, there is provided, acellular communication system. The cellular communication system isarranged to support a single cell identifier reuse pattern using a firstcommunication. Management logic comprises broadcast mode logic arrangedto support a common cell identifier reuse pattern for broadcasttransmissions amongst a cluster of communication cells using a secondcommunication. A plurality of wireless serving communication units areoperably coupled to the management logic. At least one wirelesscommunication unit comprises logic arranged to support a unicastcommunication using a first communication cell identifier and logicarranged to support broadcast communication using a common cellidentifier to be used by the wireless communication unit in receivingbroadcast communication across the cluster of communication cells.

In arranging the broadcast mode logic to apply a common cell identifierassociated with broadcast transmissions to be used on a plurality ofcells and therefore via a plurality of respective wireless servingcommunication units, one embodiment of the invention avoids handover ofcommunication when a wireless subscriber communication unit receivingonly broadcast communications roams from one wireless servingcommunication unit to another.

The invention may allow improved use of the communication resource inthe communication system, for example by more efficient use of thedownlink resource to reflect user's needs. The invention may allowimproved performance as perceived by the end-users for example byreduced interruption of downlink broadcasts when roaming. The inventionmay provide increased throughput rates, for example, due to a reductionin handover signalling. The invention may allow improved performance ina cellular network by allowing the wireless subscriber units to receivea stronger desired broadcast signal and a weaker interference signal.

The invention may allow a cellular communication system to dynamicallyuse its resources for either broadcast or uni-cast services as requiredat any time. The invention may be compatible with some existingcommunication systems, such as 3GPP TD-CDMA or TD-SCDMA cellularcommunication systems.

According to an optional feature of the invention, the management logicmay be arranged to allocate the common cell identifier to each downlinktransmission resource in all clusters of communication cells in thesecond cellular network, thereby configuring or re-configuring one ormore of the plurality of wireless serving communication units to supportbroadcast communication in the second cellular network. In this manner,the multiple cells transmitting the broadcast signal are ‘seen’ as asingle composite cell at the wireless subscriber communication unit witha greater signal power and reduced interference.

According to an optional feature of the invention, the management logicmay comprise mapping logic arranged to map the common cell identifier toat least one scrambling code and at least one pilot sequence to be usedin the cluster of communication cells.

According to an optional feature of the invention, the second cellularnetwork may be arranged to employ a carrier intended for time divisionduplex in broadcast downlink communications. For example, the firstcarrier frequency and second carrier frequency may be the same carrierfrequency, such that the first cellular network may employ a first timeportion on the carrier frequency and the second cellular network mayemploy a second time portion for broadcast downlink communications.

According to a second aspect of the invention, there is provided awireless communication unit comprising: logic arranged to support aunicast communication using a first communication cell identifier; andlogic arranged to support broadcast communication using a common cellidentifier reuse pattern for broadcast transmissions across a cluster ofbroadcast communication cells.

In one optional embodiment, the logic is arranged to support a unicastcommunication using a first communication cell identifier communicatesin a first mode of operation and the logic arranged to support broadcastcommunication using a common cell identifier reuse pattern communicatesin a second mode of operation and is adapted to tolerate a highermultipath delay of received signals than the logic arranged tocommunicate in the first mode of operation.

According to a third aspect of the invention, there is provided a methodof communicating in a cellular communication system. The methodcomprises, at a wireless communication unit, supporting a unicastcommunication using a single cell identifier reuse pattern and receivinga broadcast communications using a common cell identifier reuse patternfor broadcast transmissions across a cluster of broadcast communicationcells.

In a fourth aspect of the invention, there is provided a non-transitorycomputer program product having executable program code stored thereinfor supporting communications in a cellular communication system, theprogram code operable for, when executed at a wireless communicationunit, performing the method of the third aspect.

These and other aspects, features and advantages of the invention willbe apparent from, and elucidated with reference to, the embodiment(s)described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only,with reference to the accompanying drawings, in which

FIG. 1 illustrates a 3GPP cellular communication system adapted inaccordance with some embodiments of the present invention;

FIG. 2 illustrates cell ID allocation in a UTRA-TDD network for bothstandard uni-cast transmissions as well as combined broadcast anduni-cast transmissions in accordance with some embodiments of theinvention;

FIG. 3 illustrates a code versus timeslot diagram for a TD-CDMA cellularsystem, such as UTRA-TDD, in accordance with some embodiments of theinvention;

FIG. 4 illustrates equivalent channel profiles associated with broadcastsignals from two Node-Bs in accordance with some embodiments of theinvention; and

FIG. 5 illustrates a method of employing a combined broadcast anduni-cast operation in a cellular system in accordance with someembodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The following description focuses on embodiments of the inventionapplicable to a UMTS (Universal Mobile Telecommunication System)cellular communication system and in particular to a UMTS TerrestrialRadio Access Network (UTRAN) operating in a Time Division Duplex (TDD)mode within a 3^(rd) generation partnership project (3GPP) system.However, it will be appreciated that the invention is not limited tothis particular cellular communication system, but may be applied toother TDD-based cellular communication systems.

Referring now to FIG. 1, a cellular-based communication system 100 isshown in outline, in accordance with one embodiment of the presentinvention. In this embodiment, the cellular-based communication system100 is compliant with, and contains network elements capable ofoperating over, an universal mobile telecommunication system (UMTS)air-interface. In particular, the embodiment relates to the ThirdGeneration Partnership Project (3GPP) specification for wide-bandcode-division multiple access (WCDMA), time-division code-divisionmultiple access (TD-CDMA) and time-division synchronous code-divisionmultiple access (TD-SCDMA) standard relating to the UTRAN radioInterface (described in the 3GPP TS 25.xxx series of specifications).

In particular, the 3GPP system is adapted to support both broadcast anduni-cast UTRA communication from one or more cells.

A plurality of wireless subscriber communication units/terminals (oruser equipment (UE) in UMTS nomenclature) 114, 116 communicate overradio links 119, 120 with a plurality of base transceiver stations,referred to under UMTS terminology as Node-Bs, 124, 126. The systemcomprises many other UEs and Node-Bs, which for clarity purposes are notshown.

The wireless communication system, sometimes referred to as a NetworkOperator's Network Domain, is connected to an external network 134, forexample the Internet. The Network Operator's Network Domain includes:

(i) A core network, namely at least one Gateway General Packet RadioSystem (GPRS) Support Node (GGSN) (not shown) and at least one ServingGPRS Support Nodes (SGSN) 142, 144; and

(ii) An access network, namely:

-   -   (i) A UMTS Radio network controller (RNC) 136, 140; and    -   (ii) A UMTS Node-B 124, 126.

The GGSN (not shown) or SGSN 142, 144 is responsible for UMTSinterfacing with a Public network, for example a Public Switched DataNetwork (PSDN) (such as the Internet) 134 or a Public Switched TelephoneNetwork (PSTN). The SGSN 142, 144 performs a routing and tunnellingfunction for traffic, whilst a GGSN links to external packet networks.

The Node-Bs 124, 126 are connected to external networks, through RadioNetwork Controller stations (RNC), including the RNCs 136, 140 andmobile switching centres (MSCs), such as SGSN 144. A cellularcommunication system will typically have a large number of suchinfrastructure elements where, for clarity purposes, only a limitednumber are shown in FIG. 1.

Each Node-B 124, 126 contains one or more transceiver units andcommunicates with the rest of the cell-based system infrastructure viaan I_(ub) interface, as defined in the UMTS specification.

In accordance with one embodiment of the present invention, a firstwireless serving communication unit (e.g. Node-B 124) supports TDDoperation on a frequency channel comprising a plurality of uplinktransmission resources divided into uplink timeslots and a plurality ofdownlink transmission resources divided into downlink timeslots. Node-B124 supports communication over geographic area 185.

In accordance with one embodiment of the present invention, a secondwireless serving communication unit (i.e. Node-B 126) supports TDDoperation on a second frequency channel comprising a plurality of uplinksecond transmission resources divided into uplink timeslots and aplurality of downlink second transmission resources divided intodownlink timeslots. Node-B 126 supports communication over geographicarea 190.

Each RNC 136, 140 may control one or more Node-Bs 124, 126. Each SGSN142, 144 provides a gateway to the external network 134. The Operationsand Management Centre (OMC) 146 is operably connected to RNCs 136, 140and Node-Bs 124, 126. The OMC 146 comprises processing functions (notshown) and logic functionality 152 in order to administer and managesections of the cellular communication system 100, as is understood bythose skilled in the art.

In accordance with one embodiment of the present invention, the OMC 146(or equivalent Network Element Manager or controller with similarfunctionality) has been adapted as described below. Hereafter, this‘central’ management entity of the wireless communication system will bereferred to as ‘management logic’. The management logic 146 communicateswith one or more RNCs 136, 140, which in turn provide the signalling158, 160 to the Node-Bs and to the UEs regarding radio bearer setup,i.e. those physical communication resources that are to be used forbroadcast and uni-cast transmissions.

In accordance with one embodiment of the invention, the management logic146 has been adapted to comprise, or be operably coupled to, broadcastmode logic 150. The broadcast mode logic 150 comprises or is operablycoupled to signalling logic for signalling to the plurality of wirelesssubscriber communication units that part or all of the transmissionresource in the cellular communication system 100 is to be configured orre-configured for broadcast mode of operation. The broadcast mode ofoperation is arranged to be in addition to, or as an alternative to,uni-cast transmissions.

In one embodiment of the present invention, a wireless servingcommunication unit, such as a Node-B, comprises a transmitter that isoperably coupled to a processor 196 and a timer 192. Embodiments of theinvention utilize the processor 196 and timer 192 to configure orre-configure transmissions from the Node-B 124 in a broadcast mode.

The processor 196 supports downlink broadcast transmissions in additionto, or as an alternative to, uni-cast transmissions in either or both ofthe downlink and uplink channels of the communication system.

The timer 192 is configured to schedule complete timeslots as broadcasttransmissions, under the guidance/instruction of the broadcast modelogic 150. In one embodiment, the broadcast mode logic 150 may schedulespecial broadcast timeslots in addition to uni-cast transmissions.

The broadcast mode logic 150 is configured to manage the physicalresources that are signaled to the RNCs and the Node Bs. In this manner,the broadcast mode logic 150 allocates timeslots for broadcast, setstransit powers and allocates a single cell ID for all timeslots that areto carry broadcast transmissions.

In UTRA TDD, the concept of a single cell identifier is known, whereby anumber of identifiers are configured to identify a respective individualcell. In accordance with one embodiment of the invention the ‘singlecell identifier’ is modified and used as a ‘common cell’ identifier thatis applied across multiple cells.

Notably, the cell identifier is a parameter that may be set within thesmallest possible time allocated resource unit, for example on a pertimeslot basis in a 3GPP TDD scenario. Thus, for broadcast timeslots allcells in the 3GPP TDD network would be signalled using the sameidentifier; whilst for non-broadcast timeslots a traditionalnon-overlapping pattern of cell identifiers would be used.

It is envisaged that the broadcast mode logic 150 may also be operablycoupled to, or located within, other architecture elements within thenetwork, such as RNC 136, 140 or, say, Node-B 124. It is envisaged thatthe broadcast mode logic 150 may be distal from the OMC 146 and/or itsfunctionality may be distributed between a number of system elements.

In accordance with one embodiment of the present invention, it isproposed that the broadcast mode logic 150 allocates a data field in theexisting UTRA signalling to support combined broadcast and uni-casttransmissions. In this embodiment, as illustrated in the cell diagram200 of FIG. 2, a common cell-ID 215 is used to signify broadcasttransmission in one or a plurality of available timeslots across anumber of cells 210 supporting broadcast transmissions.

Currently in UTRA TDD, each Node B is signalled with the cell ID that itis to apply to all of its timeslots. The UEs derive the cell ID as partof their synchronisation procedure (i.e. UEs require the cell ID todecode the transmissions), which is then used to decode all of thetimeslots. In the context of the aforementioned broadcastimplementation, the cell ID of the timeslot containing thesynchronisation burst—usually the beacon timeslot—is derived in theusual manner, i.e. via the synchronisation procedure. However, once thecommon cell ID has been decoded, the UE will decode the broadcastcontrol channel (BCCH) and extract system information therefrom.Included within the system information is additional signalling (i.e.additional to the current UTRA TDD) that informs the UE of thosetimeslots that are broadcast, and hence those timeslots to use thecommon cell ID parameter in order to decode the broadcast transmissions.

FIG. 2 illustrates the broadcast transmissions being performed in allcells, using the common cell-ID 215. However, it is envisaged in anotherembodiment that clusters of cells may be configured or re-configured tosupport broadcast transmissions, in contrast to re-configuring allcells. In this manner, the cellular system supports a common cell-IDbroadcast network.

It can be further understood that, in some instances, all of the timeportion may be dedicated to broadcast transmissions. For example, withreference to the embodiment of UTRA TDD (but not limited to this case),all timeslots may be used to carry broadcast signals, i.e. with thisembodiment a common cell ID can be allocated in all of the timeslots.This broadcast mode of operation, using a single cell ID, providesparticular advantages where a wireless communication unit is roamingbetween coverage areas where uni-cast communication was previouslysupported by alternative Node Bs. In effect, the use of a common cell IDenables the roaming wireless communication unit to avoid a need toperform ‘handover’ type procedures for reception of broadcasttransmissions when roaming from the coverage region of one cell toanother.

With respect to one embodiment of the present invention, the ratio oftimeslots used for uni-cast and broadcast transmissions may beconfigured as flexible and can be dynamically altered by the broadcastmode logic 150 located within, or operably coupled to the managementlogic 146. This may be signalled either in-band, i.e. using one of theUTRA-TDD signalling channels, or out of band, i.e. using some otherradio access technology such as GPRS or UTRA-FDD for example. In thiscase, where system resources are divided between uni-cast and broadcastmodes of operation, handover functionality is still required and may besignalled, say, on a common control channel. A common control channel isselected as it is a cell-wide transmission that is intended to provideuseful system information to all UEs connected to a particular cell.

Consequently flexible broadcast deployments can be planned where, forinstance, the number of broadcast timeslots is changed either on anetwork by network approach at deployment or based upon some othercriteria such as user demand, time of day etc. For instance it may bethat more timeslots are used to convey broadcast channels in theevening, whilst during the day it may be that fewer timeslots arerequired for broadcast and more are required for uni-cast services, suchas voice telephony, broadband data applications, etc. Thus, the OMCutilises the system information that can be obtained from variouslocations within the system or supported by the system (such asscheduling of transmissions), and via various mechanisms, as known tothose skilled in the art.

As such the number of timeslots used for broadcast transmissions can beunderstood to vary from ‘0’ (no broadcast transmissions) to ‘15’ (i.e.the maximum number of timeslots in a radio frame in UTRA TDD). In thelatter example, as all available timeslots are used for broadcasttransmissions, then any additional signalling required for, say,registration and authentication could be carried on a separate radioaccess technology (e.g. GPRS or UTRA-FDD, for example) or on the sameradio access technology but at a separate carrier frequency or on analternative TDD carrier. Thus, with all ‘15’ timeslots used forbroadcast services the UTRA-TDD carrier could be considered anadditional cellular network (or carrier frequency) used in conjunctionwith an existing cellular network (or carrier frequency) as a dedicatedbroadcast carrier.

Even in such a dedicated broadcast mode of operation, it is envisagedthat certain uni-cast transmissions may still be performed, from time totime, for example to aid with authentication or registration. However,it will be appreciated that these can be performed ‘out-of-band’, forexample using another cellular network access technology, such as GPRS,FDD, etc. Alternatively, it is envisaged that the signalling may becarried out ‘in-band’ on the same TDD carrier with different allocatedtimeslots.

With regards to the receiver configuration, it is envisaged that, in thecase of ‘out-of-band’ signalling then the terminal will likely, but notnecessarily, be configured as a dual-mode device, i.e. TDD/FDD orTDD/GPRS etc.

Thus, in this aspect of the invention and with reference to UTRA TDD,all of the timeslots within a radio frame are dedicated to broadcasttransmissions, whilst any point-to-point transmissions required arecarried on another radio access technology.

The common cell-ID 215 in FIG. 2 is used in contrast to the known use ofa single cell-ID re-use pattern 220 for uni-cast timeslots 225.Basically, in UTRA TDD there is a one-to-one mapping between the cell IDand the scrambling code, and also between the cell ID and the basicmidamble code used. Thus, effectively, the cell ID is a mechanism bywhich a subscriber unit is able to differentiate between different cellsin the network.

If uni-cast and broadcast transmissions are segregated into differenttimeslots, in an UTRA-TDD network as shown in the left hand side of FIG.2, then a common cell parameter ID (denoted ‘J’) may be used across thenetwork for all broadcast timeslots. This is in contrast to a‘conventional’ uni-cast single cell parameter ID reuse plan (for exampleusing seven cell parameter IDs denoted I₁, I₂, . . . , I₇) 225, as shownin the second cell configuration 220 of FIG. 2.

In an UTRA TDD network, the cell parameter ID determines the spreadingsequences (through control of the cell ID specific scrambling sequenceapplied to the orthogonal variable spreading factor (OVSF)channelisation codes) and the pilot/midamble sequences used fortransmission in a cell. Thus, configuring all cells in the network touse the same cell parameter ID will ensure that the same spreading codesare used throughout the network in broadcast timeslots, and henceexactly the same signals will be transmitted from all cell transmittersin the network.

Furthermore, the use of a common cell ID parameter for all broadcasttimeslots in the network ensures that a common set of pilot/midamblesequences, used for channel estimation, are also used in thesetimeslots. In this manner, provision of a common cell ID allowsreception of combined signals from multiple cell transmitters. Hence, asimple receiver architecture, which would typically be employed fordetection of signals from a single source only, can be used to receivethe same signal from multiple sources. It will be understood that, inthis regard, the receiver at the wireless subscriber unit would bedesigned to cope with the time dispersion associated with receivingmultiple identical transmissions from different wireless servingcommunication units.

Thus, in this embodiment of the invention the cellular network, orcarrier of a network, carrying broadcast transmissions is configured asa dedicated broadcast transmission network/carrier. All additionalreceiver functionality to accommodate uni-cast transmission is performedusing another radio access technology or the same radio accesstechnology but on a separate carrier frequency. Thus, in thisembodiment, a dual mode device will be used. However, it is envisagedthat the device does not necessarily have to have full dual-modefunctionality.

In a further embodiment of the present invention, a partition of thephysical resources between uni-cast and broadcast transmissions may beintroduced, as illustrated in the conceptual diagram 300 of FIG. 3. Inthis embodiment of the present invention, the cellular network deliversdownlink broadcast services 335 in addition to uni-cast services 330,340 provided in both uplink and downlink directions.

Notably, whilst uni-cast services 330, 340 are delivered overnon-overlapping physical resources in adjacent cells, as in conventionalcellular systems, broadcast services 335 are also transmittedsimultaneously, i.e. in the same timeslots 350 using identical physicalresources in multiple cells. The broadcast services 335 are providedsimultaneously by either all cells in the network, or by a cluster ofcells in close proximity to one another.

For example, in one embodiment in a TD-CDMA based cellular system, suchas UTRA-TDD, the broadcast services are transmitted over the entirenetwork or over a cluster of cells using the same spreading code(s) 310,whilst uni-cast traffic is transmitted using other distinct spreadingcodes in adjacent cells. In a 3GPP context, the spreading codes may beclassified as identical or distinct by their combination with identicalor distinct cell scrambling codes (controlled via the common cell ID).

In an enhanced embodiment, it is envisaged that the portion of time usedfor uni-cast and broadcast transmissions from a network is dynamicallycontrollable by the broadcast mode logic and may vary. Advantageously,the timing of these transmissions will also be signalled to the wirelesssubscriber communication units. In this manner, the use of broadcasttransmissions over the conventional cellular network can be increased ordecreased dependent upon the prevailing conditions, such as time of day,number of active users, active user profiles, services being supported,etc.

In yet another embodiment of the present invention, broadcast anduni-cast transmissions may be allocated in different timeslots 350 inUTRA TDD (or ‘sub-frames’ in proposed long term evolutions to the UTRAstandard), as also illustrated in FIG. 3. This reduces the interferenceexperienced by the mobile receiver whilst receiving and detectingbroadcast signals. FIG. 3 shows uni-cast services 330, 340 and commonbroadcast services 335 transmitted from a first UTRA-TDD cell 315 and asecond UTRA-TDD cell 320. The first and the last timeslots are used foruni-cast transmissions 330, 340 while broadcast signals 335 aretransmitted on the three timeslots in the middle. A number of databursts, depicted in FIG. 3 by rectangular blocks, are transmitted ineach timeslot. In the uni-cast transmission 330, 340, each cell uses adistinct set of spreading codes 310 to transmit multiple bursts within atimeslot. On the other hand, bursts carrying common broadcast signals335 are transmitted from both cells 315, 320 using identical sets ofspreading codes 310. Again, it is envisaged that the aforementioned useof spreading codes can apply to the case where the spreading codes areidentical but have been modified by use of the scrambling code, such asthe use in a 3GPP context, where the scrambling code may be differentper cell.

From a wireless subscriber communication unit's perspective, receivingbroadcast signals 335 transmitted from multiple cells 315, 320 isequivalent to receiving a single higher power signal transmitted from asingle cell that has been through a more dispersive channel 415, 430(due to different propagation delays from neighbouring cells), as shownin FIG. 4.

In the conceptual diagram 400 illustrated in FIG. 4 the wirelesssubscriber communication unit (mobile terminal) 420 receives broadcastsignals from a first Node B 405 operating in a first cell (Cell#1) 315,which is located adjacent to, or neighbouring, a second Node-B 435operating in a second cell (Cell#2) 320, which is located further awayfrom the wireless subscriber communication unit 420. The channelsconnecting both Cell#1 and Cell#2 to the wireless subscribercommunication unit 420 are temporally dispersive, as indicated by theirrespective channel impulse responses 415, 430. To the wirelesssubscriber communication unit, the broadcast signal appears to have beenthrough an effective channel whose impulse response is a combination ofthe two channel responses 440, separated by the relative propagationtime between Cell#1 and Cell#2.

The wireless subscriber communication unit 420 is able to combinebroadcast signals transmitted from a plurality of cells by performing asimple detection process, identical to the process used to detectuni-cast signals, as known to those skilled in the art.

A simple detection process is less complex and provides significantlybetter performance than known explicit signal combining techniques,where different physical resources are transmitted from a number of theplurality of cells. Since, typically, broadcast signals arriving frommultiple cells appear to have passed through a more dispersive channel440 (relative to signals arriving from a single cell 415 or 430) thewireless subscriber communication unit receiver is only needed to bedesigned such that it is able to tolerate higher multi-path delays.

As a consequence, there is no longer a need for a complex receiverarchitecture or multiple receivers with signal combining circuitry.Thus, the wireless subscriber communication unit receiver is designed totolerate a certain multipath delay, whether this is due to temporaldispersion from one transmission or due to multiple transmissions of thesame signal from different transmitters.

Advantageously, in accordance with one embodiment of the presentinvention, a conventional cellular network, which typically transmitsdifferent signals from each of the cells, can be configured orre-configured to operate in a broadcast, or pseudo-broadcast, mode ofoperation. In one embodiment, this is achieved by transmittingsimultaneously the same data on the same physical resource (e.g.channelisation codes, scrambling codes, etc. of a UTRA-TDD system), withthe same pilot sequence (midambles) from multiple cells.

In this manner, the number and position of, for instance, timeslots thatcarry broadcast transmissions across the cellular network can besignalled via suitable ‘in-band’ or ‘out-band’ signalling procedures. Byreceiving the signalling, the mobile terminal's receiver is able toconfigure its receiver architecture according to its requirement forbroadcast or uni-cast transmissions, for respective portions of time.

Referring now to FIG. 5, a flowchart 500 illustrates a method ofoperating an uni-cast cellular system to additionally, or alternatively,operate in a broadcast mode of operation. At some point, for example atinitial deployment or at a later stage in the use of the network, adecision is made for the network to be used to support broadcasttransmissions, as shown in step 505.

If the answer is ‘YES’, in step 505, then a determination of therequired bandwidth of the broadcast transmission is made, as shown instep 510. This determines, amongst other parameters, how many timeslotsare required for the broadcast transmission. The broadcast mode logicthen sets a common cell ID for the selected timeslots, as shown in step515. This is signalled to the Radio Network Controller, which in turnsignals the information to the Node-Bs and the UEs.

It is also envisaged that the bandwidth of the broadcast transmissioncan be dynamically adjusted by the network side (e.g. the OMC) as it isa broadcast service. In this manner, more slots may be allocated tobroadcast transmissions during peak times or as a result of news events,etc., as in step 525, or following a determination that the broadcasttransmission bandwidth is sub-optimal, in step 520. It is envisaged thata change of bandwidth in the system for broadcast transmissions may alsoresult in an alteration of the number of timeslots needed, and hencesignalled, for common cell ID use.

It is noteworthy that the above embodiments, which propose use of acommon cell ID to identify broadcast transmissions, are not supportablewithin the present UTRA TDD standard, i.e. the standard requiresamending to support the additional signalling required by the aboveembodiments. Thus, there has been no provision for such a service.

It will be appreciated that, for clarity purposes, the above descriptionhas described embodiments of the invention with reference to differentfunctional units and processors. However, it will be apparent that anysuitable distribution of functionality between different functionalunits or processors, for example with respect to the broadcast modelogic or management logic, may be used without detracting from theinvention. For example, functionality illustrated to be performed byseparate processors or controllers may be performed by the sameprocessor or controller. Hence, references to specific functional unitsare only to be seen as references to suitable means for providing thedescribed functionality, rather than indicative of a strict logical orphysical structure or organization.

Aspects of the invention may be implemented in any suitable formincluding hardware, software, firmware or any combination of these. Theinvention may optionally be implemented, at least partly, as computersoftware running on one or more data processors and/or digital signalprocessors. Thus, the elements and components of an embodiment of theinvention may be physically, functionally and logically implemented inany suitable way. Indeed, the functionality may be implemented in asingle unit, in a plurality of units or as part of other functionalunits.

Although one embodiment of the invention describes broadcast mode forUTRA TDD it is envisaged that the inventive concept is not restricted tothis embodiment. In particular, for example, future evolutions of UTRA3GPP (currently referred to as ‘long term evolution’ (LTE)) will also bedivided into timeslots (or other such named time portions), and willtherefore be able to benefit from the concepts described hereinbefore.

Delivering broadcast services over cellular networks, in the mannerdescribed above, is extremely attractive, for at least one or more ofthe following reasons:

(i) It provides a self-contained communication system, for example thesignalling required (e.g. for encryption key exchange) and uplink data(e.g. to support interactive services) can be carried by the same systemthat is used to deliver the downlink broadcast service.

(ii) It allows a cellular operator to reuse existing uni-castinfrastructure to provide a dynamic ‘broadcast/uni-cast’ combinationservice.

(iii) Improved spectral-efficiency of a cellular communication systemcan be achieved by delivering a combination of broadcast and uni-castservices.

(iv) It allows a cellular operator to use spectrum that they already ownfor a new service, thereby facilitating a new revenue stream from theirusers.

(v) It significantly reduces the cost of the wireless subscribercommunication unit if both broadcast and ‘conventional’ uni-castservices are delivered over the same (or compatible) radio accesstechnologies.

(vi) A wireless subscriber communication unit receiving in timeslotsallocated for broadcast transmission sees a much stronger compositebroadcast signal sent from several cells, instead of a single celltransmission with several interfering transmissions from other cells(and hence other cell IDs). Thus, the SNR seen in the broadcasttimeslots is improved thereby facilitating higher sustainable throughputrates. Thus, the inventive concept provides a more efficient mechanismfor delivering broadcast content to the wireless subscriber units.

(vii) A yet further advantage is that one embodiment of the inventionuses a radio access technology that is divided into timeslots, such asUTRA TDD or 3GPP LTE. Thus, when configuring or re-configuring thecommunication system to operate in a broadcast mode or a partialbroadcast mode of operation, it is possible to exploit the inherenttimeslot nature to provide ‘discontinuous’ reception, i.e. sometimeslots can be used whilst others are not. In this manner, asignificant conservation in the battery life of the wireless subscribercommunication unit can be achieved, when compared with, say, applyingthe same principal to a WCDMA network.

Although the present invention has been described in connection withsome embodiments, it is not intended to be limited to the specific formset forth herein. Rather, the scope of the present invention is limitedonly by the accompanying claims. Additionally, although a feature mayappear to be described in connection with particular embodiments, oneskilled in the art would recognize that various features of thedescribed embodiments may be combined in accordance with the invention.In the claims, the term ‘comprising’ does not exclude the presence ofother elements or steps.

Furthermore, although individually listed, a plurality of means,elements or method steps may be implemented by, for example, a singleunit or processor. Additionally, although individual features may beincluded in different claims, these may possibly be advantageouslycombined, and the inclusion in different claims does not imply that acombination of features is not feasible and/or advantageous. Also, theinclusion of a feature in one category of claims does not imply alimitation to this category, but rather indicates that the feature isequally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply anyspecific order in which the features must be performed and in particularthe order of individual steps in a method claim does not imply that thesteps must be performed in this order. Rather, the steps may beperformed in any suitable order. In addition, singular references do notexclude a plurality. Thus, references to “a”, “an”, “first”, “second”etc. do not preclude a plurality.

We claim:
 1. A cellular communication system (100) arranged to support asingle cell identifier reuse pattern using a first communication; thecellular communication system (100) comprising: management logic (146)having broadcast mode logic (150) arranged to support a common cellidentifier reuse pattern for broadcast transmissions amongst a clusterof communication cells using a second communication; a plurality ofwireless serving communication units operably coupled to the managementlogic; and at least one wireless communication unit comprising logicarranged to support unicast communication using a first communicationcell identifier and logic arranged to support broadcast communicationusing a common cell identifier (215) to be used by the wirelesscommunication unit in receiving broadcast communication across thecluster of communication cells.
 2. The communication system of claim 1wherein the at least one wireless communication unit is arranged to usethe common cell identifier in each downlink transmission resource in allclusters of communication cells to support receiving of the broadcastcommunication.
 3. The communication system of claim 1 wherein the commoncell identifier is mapped to at least one scrambling code and at leastone pilot sequence to be used in the cluster of communication cells bythe at least one wireless communication unit.
 4. The communicationsystem of claim 1 wherein the at least one wireless communication unitfurther comprises a receiver for receiving signalling information thatindicates a timing of the unicast communication transmissions and atiming of the broadcast communication.
 5. The communication system ofclaim 1 wherein the broadcast communication is arranged to employ acarrier intended for time division duplex in broadcast downlinkcommunications.
 6. The communication system of claim 1 wherein the firstcommunication employs a first carrier frequency and the secondcommunication employs a second carrier frequency to broadcast downlinkcommunications.
 7. The communication system of claim 6 wherein the firstcarrier frequency and second carrier frequency are the same carrierfrequency such that the first communication employs a first time portionon the carrier frequency and the second cellular network employs asecond time portion for broadcast downlink communications.
 8. A wirelesscommunication unit comprising: logic arranged to support a unicastcommunication using a first communication cell identifier; and logicarranged to support broadcast communication using a common cellidentifier reuse pattern for broadcast transmissions across a cluster ofbroadcast communication cells.
 9. The wireless communication unit ofclaim 8 wherein the logic arranged to support a unicast communicationusing a first communication cell identifier communicates in a first modeof operation and the logic arranged to support broadcast communicationusing a common cell identifier reuse pattern communicates in a secondmode of operation and is adapted to tolerate a higher multipath delay ofreceived signals than the logic arranged to communicate in the firstmode of operation.
 10. The wireless communication unit of claim 8wherein the wireless communication unit comprises a receiver forreceiving signalling information that indicates a timing of the unicastcommunication transmissions and a timing of the broadcast communicationusing the common cell identifier reuse pattern.
 11. The wirelesscommunication unit of claim 8 wherein the logic arranged to support aunicast communication using a first communication cell identifier andthe logic arranged to support broadcast communication using a commoncell identifier reuse pattern are dynamically re-configured to supportan increase or decrease of the broadcast communication dependent upon atleast one prevailing communication condition.
 12. The wirelesscommunication unit of claim 11 wherein the at least one prevailingcommunication condition comprises at least one from a group consistingof: a time of day, a number of active users, active user profiles,services being supported.
 13. The wireless communication unit of claim 8wherein the broadcast communication and the unicast transmissions areallocated different timeslots (350) or different sub-frames.
 14. Amethod of communicating in a cellular communication system, the methodcomprising, at a wireless communication unit: supporting a unicastcommunication using a single cell identifier reuse pattern; receivingbroadcast communication using a common cell identifier reuse pattern forbroadcast transmissions across a cluster of broadcast communicationcells.
 15. A non-transitory computer program product having executableprogram code stored therein for supporting communications in a cellularcommunication system, the program code operable for, when executed at awireless communication unit: supporting a unicast communication using asingle cell identifier reuse pattern; and receiving broadcastcommunication using a common cell identifier reuse pattern for broadcasttransmissions across a cluster of broadcast communication cells.